The speed of input/output signals of a CPU (Central Processing Unit) incorporated in a computer is getting higher along with improving performance of a computer. Therefore, avoiding the attenuation of a high speed signal propagating on a circuit board is an issue to be addressed. In order to cope with this issue, consideration about a method to input and output a high speed signal of a CPU using a photoelectric conversion module (hereinafter, referred to as “optical module”) is progressing in recent years. An optical module has a function to convert an electric signal and an optical signal from one into the other or in a mutual manner. In measures against the attenuation of a high speed signal using an optical module, the feature that the attenuation of a light signal is smaller than that of an electric signal is utilized. That is, in part of the entire signal line through which a high-speed input/output electric signal is transmitted, converting an electric signal into a light signal using an optical module to transmit the light signal suppresses the attenuation of a high speed signal on a circuit board.
In order to improve the effect obtained by converting a high-speed electric signal of a CPU into a light signal to transmit the light signal, the attenuation of an electric signal on a circuit board needs to be decreased as much as possible. Accordingly, it is required that the length of sections of a circuit board where a transmitted signal propagates as an electric signal is reduced as short as possible. An optical module needs to be mounted near the CPU as close as possible. The number of input/output signals of the CPU reaches several hundreds to several thousands in a super computer. Therefore, a large number of very small optical modules are needed to be mounted in high density on a circuit board.
An optical module which receives and outputs light in a direction parallel to a circuit board is disclosed in Japanese Patent Application Laid-Open No. 2008-41770 (hereinafter, referred to as patent document 1). In this optical module, an optical fiber is taken out from a side surface of the module in a direction parallel to a circuit board onto which the optical module is mounted.
An optical module which receives and outputs light in a direction vertical to a circuit board is disclosed in Japanese Patent Application Laid-Open No. 2008-34622 (hereinafter, referred to as patent document 2). This optical module is mounted on a circuit board with an opening. Light from a light emitting device in an optical module is radiated vertically to a circuit board in the direction of the rear surface of the circuit board through the opening.
In I. Hatakeyama, et al.: “Optical Module Technology for High-speed Interconnections-System LSI Module with Optical I/O Interfaces”, OPTRONICS Magazine, No. 277, p. 184 (Jan. 10, 2005), an optical module which receives and outputs light in a direction vertical to a circuit board is also described (hereinafter, referred to as “non-patent document”). FIG. 29 is a sectional view showing the structure of the optical module disclosed in the non-patent document. In this module, an optical device 2902 and an optical device driver IC 2903 are mounted onto a transparent resin board 2901. The optical device 2902 and the optical device driver IC 2903 are covered with a metal casing 2904. A lens supporter 2905 is joined to the surface of the transparent resin board 2901 opposite to the surface onto which the optical device 2902 is mounted. A flat-plate micro lens array 2906 is incorporated in the lens supporter 2905. A light signal 2907 emitted or received by the optical device 2902 is outputted or inputted between the outside and the inside of the optical module via the flat-plate micro lens array 2906. The light signal 2907 is inputted or outputted between the outside and the inside of the optical module by connecting an optical fiber optically.